The present invention relates to methods of predicting the occurrence of seismic events from changes in the earth""s equipotential gravitational surface due to polar motion. More particularly, accumulated gravitation shift in geoids between successive polar motions is associated with the accumulation in energy in the earth""s crust which can be correlated to seismic events.
The majority and most destructive of earthquakes or seismic events are the tectonic quakes which are a result of a sudden release of energy accompanying a shift or dislocation of the earth""s crust (shallow) and in the upper mantle (deep).
Shifts in the earth""s crust create a potential energy, which is occasionally released in a seismic event. Due to the devastating results of earthquakes, particularly those occurring in populated areas, there have been concerted efforts to predict such events.
There are known areas of frequent seismic activity such as geological locations having faults. Monitoring stations are provided at these locations which, at best, provide warning of an immediately impending event. Monitoring primarily consists of recording geophysical precursors such as P-wave velocity, ground uplift, radon emission, rock electrical resistivity and water level fluctuations. These precursors can have lead times of one day through to several years depending upon the magnitude of the upcoming event.
Some approaches to obtaining more advance notice or prediction of future events includes statistical analysis of the history of earthquakes in a given location so as to determine whether there is a recurrent, or cyclical pattern to the events. These methods can provide a statistical value, for example, a 70% probability of an event happening every 100 years, but still leave an uncertainty of tens of years.
Generally however, there is a need for an earlier warning system and one which can be tied to known and independent factors.
Using the motion of the earth""s poles, a series of successive geoids can be determined. The shift between incremental geoids provides information necessary to determine changes in gravitational anomalies and ultimately the accumulation in energy at a given geological location. Knowing the energy which was released in a previous seismic event, the geoidal shift method of the present invention can be used to monitor and predict a subsequent seismic event.
In a broad form of the invention, a method is provided for predicting seismic events comprising: determining a first geoid surface at first instance in time; determining successive geoid surfaces for successive and incremental instances in time; determining an incremental energy associated with each incremental shift between the successive geoid surfaces; accumulating energy associated with the incremental shifts; and comparing the accumulated energy with a pre-determined energy which has resulted in a seismic event as being indicative of the likelihood of a future seismic event. Preferably, the pre-determined energy for a seismic event is determined by establishing measures of the energy released in a previous seismic event.